The present invention relates to tip clearance control, and more particularly to a cored case structure for active tip clearance control in a gas turbine engine.
Gas turbine engine rotor blade tip clearances have a significant influence on engine performance. When clearance between blade tip and case is controlled, leakage past the blade tips is minimized for efficient cruise flight, yet clearance can be selectively increased during other portions of the flight so as to avoid blade tip rub. Thrust specific fuel consumption of the engine is thereby reduced and engine durability is increased.
Systems that control blade clearance are typically referred to as active clearance control (ACC) systems. Active clearance control systems cool certain areas of the engine case to shrink the engine case around the rotating compressor blades to thereby minimize the clearance between the case and blade tips. One conventional method for ACC utilizes ducts external to the engine case which impinge relatively cool air on case rails which project from the gas turbine engine turbine case. The relatively cool fan air may be scooped from the fan stream or secondary flow and communicated through the ducts.
Although effective, the external ACC ducts and case rails may increase weight and complexity of the engine.
Accordingly, it is desirable to provide an uncomplicated and light weight active clearance control cooling system.